1. Field of the Invention
The invention relates to a hydraulic rotary/rotation damper with built-in pressure equalization that is intended for use on a multiwheeled vehicle or on a vehicle with runners, such as a motor cycle, an ATV or a snow scooter. The damper comprises an outer housing in which an oil chamber is configured. The oil chamber is divided into two chambers by a delimiting arm/blade that is rotatable about a first end. At the first end of the arm is a lever that rotates with the delimiting arm relative to the outer housing. The oil flow between the two damping chambers differs depending upon whether the delimiting arm is rotating from a central position outward toward an outer position or from the outer position and inward toward the central position. In addition, the oil flow between the two damping chambers is adjusted with a valve through which the flow varies with the flow velocity.
2. Description of the Related Art
A rotary damper can be fitted between the rotary handlebar of a vehicle and its fixed frame or chassis in order to damp shocks and violent motions that are transmitted from the front wheel(s) to the handlebar, i.e. the damper is used as a steering damper. Where the steering damper is used on a motorcycle, the steering damper can solve wobbling, which can occur in a motorcycle at high speeds. Wobbling means that the front wheel of the motorcycle begins to oscillate about the steering axle with increasing amplitude. Where the steering damper is used on a four-wheeled all-terrain vehicle, a so-called ATV, the steering damper primarily is intended to damp out violent steering motions that are caused by, for example, an asymmetric load exerted upon the wheels. This is the same for snow scooter applications. A rotation damper can also be used for other vehicle-specific applications, for example, to damp a motion between a wheel or runner and a chassis.
In a steering damper in the form of a hydraulic rotation damper, it has proven difficult to adjust the damping character in the steering damper when the driver executes a steering motion or when the handlebar moves back to the central position.
In the prior art, see, for example, published patent application US 2004/0239069, a steering damper is described in which the two damping chambers are connected by a duct containing an adjustable high-speed valve. Also connected to the duct is a pressurizing tank. Because only one valve is used and because the duct extends between the outer parts of the two damping chambers, the damping character is the same during both outward movement and inward movement of the blade.
In U.S. Pat. No. 6,802,519, a steering damper is described in which the damping chambers are connected to three different ducts depending upon whether the blade moves in an outward motion or an inward motion from the central position. When the blade moves in the outward motion, the flow between the damping chambers runs in a first duct or a second duct, whose areas are adjustable by a respective valve. When the blade moves with the inward motion, the flow between the chambers runs in a third duct that is fully open and allows free flow such that the inward motion is totally undamped. In a neutral position, i.e., when the blade is in the central position, the connection between the chambers is closed off. The drawback with this solution is, firstly, that the damping during the inward return motion is totally undamped and non-adjustable and, secondly, that the damper has no pressurization. A totally undamped return motion can produce undesirable vibrations in the system, which can result in inconsistent behavior and cavitation.
A further problem that has manifested itself in a steering damper in the form of a hydraulic rotation damper involves adjusting the flow between the damping chambers that are delimited by the rotary arm so that the damping force is adapted to different flow velocities, i.e. motions of different magnitude between the handlebar and the frame.
In the prior art, see, for example, U.S. Pat. No. 1,873,100, the damping force is adapted to different flow velocities by the use of a throttle valve, a so-called bleed valve, for example, which is placed in the damping duct between the chambers. Throttle valve means a fixedly adjustable restriction that increases the damping quadratically with the flow velocity.
In one refinement of such a steering damper, see U.S. Pat. No. 4,773,514, a traditional throttle valve has been supplemented by a further, narrower, fixed throttle valve, i.e., a so-called high-speed valve. At a predetermined high flow velocity, the narrower valve takes over the full oil flow and, thereafter, the damping follows the curve of the narrower restriction. However, this solution, too, has limitations. The narrower valve often displays a tendency to take over the full oil flow too long, resulting in an inconsistent damping character. Moreover, it is difficult to ensure consistent damping character from one damper to the next because adjustment of the valve is made before the damper is fitted. The high-speed valve is flowed through, moreover, from different directions in the event of right or left steering deflections, the effect being that the forces can only with difficulty be made equal in both directions. Because of this two-way flow through the valve, it also is a problem to adjust the return travel from the respective outer end position and to easily pressurize the steering damper such that the damper is insensitive to temperature changes.
Published patent application US 2004/0239069 describes that the steering damper electrically adjusts the damping characteristics on the basis of the steering speed. The throttling magnitude of a valve is adjusted with a linear motor so that the flow through the valve is adapted to the speed and steering speed of the vehicle. The damping characteristics are altered so that at a low speed there is a low damping force and at a high speed there is a high damping force. In addition, the damping is adjusted so that, at a speed-dependent steering speed, the slope of the damping curve is altered such that the damping force increases more slowly at increased steering speed. This slower damping force increase prevents the steering from becoming too hard at certain speeds. This damping character is suitable for road-driven motor cycles. For a versatile damper that is usable in off-road driving, the damper should be able to rapidly absorb powerful shocks caused by the ground surface and also should be able to rapidly return to the original position. A slow damping force increase therefore is not desirable. Instead, a slow damping force increase prevents these characteristics. Moreover, controlling of the damper calls for electrically controlled components, which means that the adjustment becomes complicated and prone to breakdowns and power failures.
In addition, there are also valves commonly known within hydraulics, intended for use as flow limiters, in which the restriction increases with increased flow. These valves have not previously been used, however, to adjust the damping character of a steering damper, but rather are used, for example, to adjust the flow of hydraulic medium in differentials.